Process of treating silicon steel



Patented Aug. 23 1932 UNITED "STATES PATENT OFFICE ALPHONSUS I. MURPHY AND WILLIAM JONES, OF ZANESVILLE, OHIO, ASSIGNORS TO THE AMERICAN ROLLING HILL COMPANY, OF IIDDEETOWN, OHIO, A CORPORATION" R0 Drawing. Application filed Play 18,

Our invention relates to processes for the formation of sheets of magnetic steel having a desirable surface finish, being free from scale, possessing the required magnetic propsj erties and formed of high silicon alloy steel,

containing from 1 to 6% of silicon.

In our former Patent No. 1,714,038, we have described the process which consists in giving the rolled sheets, i. e. sheets which have been reduced to gauge by any suitable rolling treatment, a pickling and a washing treatment of particular character. After-. ward the sheets are treated with a separator film, and are given a first anneal. A cold rolling is then given to the sheets followed by a second anneal.

We have discovered that a shorter process than that set forth in our Patent No. 1,714,038, may be practiced in the production of magnetic sheets with attendant economy, and a better product produced, by a difierent series of steps in which a cold rolling is 'ven to the sheets after they have been pick e d and washed, but without any intervening annealing, after which the anhealing is imparted in a single treatment, a feature of which is a very slow cooling.

We now find that pickling and washing the sheets and then immediately cold rolling them for the purpose of imparting to them desirable surface characteristics, as distinguished from efiecting any substantial reduction in thickness, and if desired, spraying the sheets with a separator substance, followed by a single anneal, will result in a very satisfactory finish on the sheets, of gray color, the sheets themselves being practically free from scale and having desirable magnetic qualities.

In preparing the sheets for our process it is understood that they may be reduced in any suitable way. They may thus be hot rolled to gauge in the usual manner, and if desired, given a cold rolling, not for the purpose of effecting any substantial reduction in gauge but in order to impart desirable surface characteristics to the product. Having been prepared in this or any other suitable manner, the sheets are then passed to the pickling bath, which may be made up of a PROCESS OF '.I.REATING SILICON STEE- 1981. Serial 1%. 538,253.

solution of sulphuric acid, as is usual in metal pickling, to which solution ma be added some one of the organic materials employed in the art for retardin hydrogen development and permittin t e scale to be lifted without rupture o the surface of the material.

When the sheets have been pickled so as to be free of scale, they are then thoroughly washed, the final washing being preferably basic so as to neutralize any remalning acid on the sheets. A solution of water and air slaked lime will serve this purpose very well, and following the neutralizing the sheets are preferably boshed or scrubbed mechanically.

The next operation is preferably a cold rolling step. The sheets while still wet, if desired, are given a skin pass in cold rolls, without attempting to effect any substantial reduction in the thickness of the sheets. The cold rolling of silicon steel in the usual type of sheet cold rolls will not elongate the sheets by any substantial amount. Cold rolling, however, makes the sheets more smooth and seems to increase the densit of a pickled material very slightly, and t ese factors result in a somewhat higherspace factor in the completely processed sheets under favorable conditions. Although the pressure of the sheet cold rolls is not greatenough to elongate the sheets, it will im rove their flatness, and it makes it possi le to pile the sheets in the annealing furnace in such a manner as to insure that they will be flat after they have been annealed with the proper heating and cooling rates.

A spraying with air slaked lime in order to apply a mechanical separating coat between the sheets may then be given to the product.

Finally, the sheets are piled and annealed, preferably in an electric furnace. It is our regular practice to remove the furnace from the charge at a temperature of approximate- 1y 1000 F., the furnace being of the bell type, and within approximately 3 minutes to re-cover the charge with a sheet metal cover to prevent too rapid cooling during the following hour or so, and also to prevent ex the sheets whic cessive oxidation. This uncovering temperature will usuall depend u on the width of are coole their resistance to oxidation, and the degree of flatness and freedom from scale desired- It cannot be increased much as otherwise a prohibitive amount of buckling of the sheets occurs during the 3-minute interval referred to. This is because of the very large difference in temperature which would exist under such conditions between the center and the edge of the sheets. However, where commercial conditions will permit, it is preferable to turn off the furnace and permit the sheets to cool down to a temperature at which they can be handled, before removing the furnace, or taking out the sheets.

The primary result of the high temperature annealing which we practice is the recrystallization of the grain structure, with the result that the rains increase in size man times and also ecome equiaxed. This furnaces otherwise heated, the same results trolled in the electric furnace.

that are obtained in the electric furnace. The waviness sometimes produced in other types of furnaces is not due to the means employed for producing heat, but is due to improper rates of heating and cooling and we have found that these factors may be readily con-- However, since electric furnaces are ordinarily very heavily insulated, the cooling rate while adequately slow for some portions of the cycle, is unnecessarily slow for other portions thereof. Hence we havesecured adequate results by the treatment hereinabove described, in which the electric furnace is removed from the sheets, and the sheets immediately covered with a sheet metal box.

The resulting product will be a smooth, clear surfaced sheet, with a very high space factor; that is to say, the proportion of solid metal to solid metal plus surface irregularities and scale or oxide in a pile made up of a number of sheets under a given pressure. Under standard tests we have made a product having a space factor of 96 and beyond, even for materials which are very high in silicon.

It will be noted by this process that it avoids an anneali step called for in our former patent, an in addition, imparts a cold rolling to the product before the surface conditions resulting from the pickling and washing treatments have been altered by an annealing treatment.

Having thus described our invention, what we claim as new and desire to secure by Let ters Patent, is

1. A process for preparing silicon steel sheets for electrical purposes which consists in pickling, neutralizing, and washing the hot-rolled silicon steel sheets, then cold rolling them to impart surface without substantial reduction in thickness, and finally annealing the sheets to impart magnetic properties.

2. A process for preparing silicon steel sheets for electrical urposes which consists in pickling, neutralizing, and washing the hot-rolled silicon steel sheets, then cold rolling them to impart surface finish without substantial reduction in thickness, coating the sheets with a separator substance, and finally annealing the sheets to impart magnetic roperties.

3. process for preparing silicon steel sheets for electrical purposes which consists in pickling, neutralizing, and washing silicon steel sheets which have been reduced to gauge, then cold rolling said sheets to impart desirable surface characteristics without substantial reduction in thickness, said cold rolling followin upon said pickling, neutralizing and was ing treatments before the surface characteristics of said sheets have been altered, and finally annealing said sheets to impart magnetic properties.

4. A process for preparing silicon steel sheets for electrical purposes which consists in pickling, neutralizing, and washing silicon steel sheets which have been reduced to gauge, then cold rolling said sheets to impart desirable surface characteristics without substantial reduction in thickness, said cold rolling following upon said pickling, neutralizing and washing treatments before the surface characteristics of said sheets have been altered, and finally annealing said sheets to impart magnetic properties, said annealing being carried on at high temperatures and characterized by slow cooling.

5. A process for preparing silicon steel sheets for electrical purposes which consists in picklin neutralizing, and washing sili con steel s eets which have been reduced to gauge, then cold rolling said sheets to impart desirable surface characteristics without substantial reduction in thickness, said cold rolling following upon said pickling, neutralizing and washing treatments before the surface characteristics of said sheets have been altered, and finally annealing said sheets to impart magnetic properties, said annealing being carried on at high temperatures and characterized by slow cooling, at least during that portion of the cooling cycle between ilggfdi ng temperature and substantially Ill Lenses 6. A process for preparing silicon steel sheets for electrical purposes which consists in pickling silicon steel sheets which have i been reduced to gauge, neutralizing and washing said sheets, immediately cold roll ing them to impart desirable surface characteristics, but without substantial reduction in gauge, coating said sheets with a mechanicalseparator, annealing said sheets in the electric furnace at high temperatures, removing said sheets from said furnace at approximately 1600 F., and immediately covering said sheets so as to reduce their rate of cool- A process for preparing silicon steel sheets for electrical purposes which consists in pickling, neutralizing, and washing silicon steel sheets which have been reduced to gauge, then cold rolling said sheets to impart desirable surface characteristics without substantial reduction in thickness, said cold rolling following upon said pickling, neutralizing and washing treatments before the surface characteristics of said sheets have been altered, and finally annealing said sheets to impart magnetic properties, said annealing being carried on at high temperatures and characterized by rates 0 temperature change, both during the heating and cooling portions of the cycle, such that the sheets are free from thermal stress and remain free from distortion and buckles.

ALPHONSUS F. MURPHY. WILLIAM JONES. 

